In recent years, secondary batteries typified by lithium ion secondary batteries have been widely used as power sources for mobile electronic devices such as cellular phones and mobile personal computers.
Now, as this secondary battery (hereinafter, also simply referred to as a “battery”), a battery has been widely used which is structured to have a laminate of multiple positive electrode members and negative electrode members stacked with separators interposed therebetween, and an electrolyte (electrolytic solution) housed in an exterior body composed of laminated sheets, and have a positive electrode lead terminal and a negative electrode lead terminal electrically connected to the positive electrode members and the negative electrode members, which are extended outward from the exterior body.
One of such batteries is a battery 100 as shown in FIGS. 6(a) and 6(b) (see Patent Document 1).
This battery 100 has a battery element 101 housed in an exterior body (packing material) 103 composed of a laminated sheet 102, and has a structure with a lead terminal 104 extended outward from the exterior body 103.
Further, this battery 100 is formed by forming parts 102a of the laminated sheet 102 in advance in outwardly convex shapes as shown in FIG. 6(a), reducing the pressure in the battery (in the exterior body) for heat sealing, and then inwardly pressing the convex parts 102a at the atmospheric pressure, thereby causing inverse deformation as shown in FIG. 6(b).
The configuration of the battery is supposed to be less likely to increase the internal pressure, excellent in safety, and able to stabilize battery characteristics over a long period of time, because the inversely deformed parts of the exterior body function as buffers for preventing the increase in internal pressure due to gas generation, thereby preventing deformation, etc. of the exterior body.
However, when the gap between the exterior body and an electrode laminate housed within the exterior body is excessively increased, the inversely deformed parts are pressed at the atmospheric pressure to undergo deformation, thereby generating a large number of shrinkage wrinkles on the exterior body. Further, the shrinkage wrinkles have the problem of causing cracks or fractures on the exterior body (packing material) to be induced, thereby even leading to seriously damaged reliability.
Patent Document 1: Japanese Patent Application Laid-Open Publication No. 2007-71133